The proposed research tests the broad claims of the information-loss model of age-related cognitive slowing proposed by Myerson, Hale, Wagstaff, Smith, and Poon (1990). The model assumes that a single factor, variations in the number of processing steps, is responsible for how response latencies are affected by task complexity, practice, fluctuations in individual performance, and shifts in the emphasis on speed versus accuracy. The model further assumes that a second factor, differences in information-processing efficiency, underlies differences in response latencies of older and younger adults. The interaction of these two factors determines the form of the relation between the latencies of older and younger adult. Establishing the relation between the latencies of older and younger adults will provide an important cognitive benchmark that can be used to determine when individual patterns of cognitive slowing are typical of healthy older adults and when such patterns are indicative of pathological changes. To study this relation, three series of experiments will examine the latencies of older and younger adults on a variety of cognitive tasks. The first series will manipulate practice and speed-accuracy tradeoff to test the hypothesis that the relation between older and younger adults' latencies remains invariant. The second series will examine individual subjects and fluctuations in their performances to test the hypothesis that information loss slows all cognitive processes in all individuals at all levels of performance. The final series will test for the existence of two cognitive domains, each with its own developmental trend with respect to cognitive slowing, and is designed to determine the factors responsible for information loss. In all three series, the predictions of the information-loss model will be compared with those of alternative models of global cognitive slowing, e.g., the multi-layered slowing model and the overhead model proposed by Cerella (1985; 1990).